Thickened fluids or gels, often referred to as isolation gels or gel plugs, have been used for several years to pack subsurface apparatus, such as spools, manifolds and sections of pipe in order to minimize the ingress of fresh water or sea water during assembly or laying of such subsurface apparatus.
Gel plugs often consist of water-based crosslinked viscosifying polymers, such as guar. Gel plugs are characterized by a high loading of viscosifying polymer, typically about 100 pounds per 1000 gallons of base fluid is used. Once the viscosifying polymer is hydrated in water, chemicals are added to adjust the pH and to crosslink the polymer. The crosslinked gel is then placed, pumped or injected into the subsurface apparatus, such as at the end of a pipe section closed by a blind flange. When the pipe sections are transported and eventually placed in their subsurface location, the installation process begins. The blind flange or other pipe and sealing device are removed exposing the end of the pipe to the open environment. The subsurface connection is then made.
At some point, the gelled material is displaced out of the subsurface assembly, either before or during the commissioning of the pipe. Methods have been sought which lessen displacement of the gelled material from the subsurface assembly.
In addition, manufacturers of subsea apparatus composed of such sensitive metals as stainless steel have increasingly demanded that the chloride level of base fluids be less than 50 ppm in light of internal parts and in order to minimize salt corrosion. Exposure of certain alloys to high chloride levels often causes intergranular stress crack corrosion (IGSCC). Alternative gelling materials have been sought which minimize salt corrosion.